🧮 Body Surface Area (BSA) Calculator
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, health content reviewer · Updated 2026-06-19
This calculator gives an estimate only and is for general information, not medical advice. Body surface area is used in clinical settings such as drug dosing, and the exact value can vary with the formula chosen and with how height and weight are measured. Do not use this result to set or change any medication dose. Always rely on a qualified clinician and the values recorded in your medical records.
Body surface area (BSA) estimates the total external area of your body, expressed in square meters. It is widely used in medicine because many clinical measures, from drug doses to cardiac output, scale better with surface area than with weight alone. Enter your height and weight in metric or imperial units, and this calculator returns your BSA using the Mosteller formula, the version most commonly used in practice because it is simple and accurate.
What is the Body Surface Area Calculator?
Body surface area is the measured or estimated area of the outer surface of the human body. Because it cannot be measured directly without elaborate equipment, it is estimated from height and weight using a formula. The result is reported in square meters, and a typical adult falls somewhere between about 1.5 and 2.0 m2. BSA matters clinically because the size of a person's surface relates more closely than body weight to physiological processes such as metabolic rate, fluid requirements and how the body handles certain drugs.
The Mosteller formula, published in 1987, is the one this tool uses. It states that BSA in square meters equals the square root of the product of height in centimeters and weight in kilograms divided by 3600. Its appeal is that it is easy to calculate by hand or on a basic calculator while staying close to older, more complex equations such as the Du Bois and Du Bois formula. For a person who is 170 cm tall and 70 kg, the Mosteller estimate is about 1.82 m2.
Different formulas exist, including Du Bois, Haycock, Gehan and George, and Boyd, and they can disagree by a few percent, especially at the extremes of height and weight or in children. None of them is a perfect measurement, since they are all statistical estimates fitted to populations. For everyday understanding and for most adult calculations the Mosteller result is more than adequate, but in clinical dosing the choice of formula and rounding rules is decided by protocol, not personal preference.
When to use it
- Understanding a BSA figure mentioned by a doctor or pharmacist, for example in chemotherapy dosing.
- Students in nursing, pharmacy or medicine practicing the Mosteller calculation for exams and coursework.
- Estimating body surface area for physiology or fitness contexts where it is used to normalize measurements.
- Comparing how BSA changes with different heights and weights to build intuition about body size.
How to use the Body Surface Area Calculator
- Choose metric (centimeters and kilograms) or imperial (feet, inches and pounds) units.
- Enter your height in the selected units.
- Enter your weight in the selected units.
- Read your body surface area in square meters from the result panel, which updates instantly.
Formula & method
Worked examples
An adult who is 170 cm tall and weighs 70 kg.
- Multiply height by weight: 170 × 70 = 11,900
- Divide by 3600: 11,900 ÷ 3600 = 3.3056
- Take the square root: sqrt(3.3056) = 1.818
- Round to two decimals: 1.82
Result: BSA ≈ 1.82 m²
A person who is 180 cm tall and weighs 80 kg.
- Multiply height by weight: 180 × 80 = 14,400
- Divide by 3600: 14,400 ÷ 3600 = 4
- Take the square root: sqrt(4) = 2
- Round to two decimals: 2.00
Result: BSA ≈ 2.00 m²
A person who is 5 ft 7 in tall and weighs 154 lb (imperial input).
- Convert height: (5 × 12 + 7) × 2.54 = 67 × 2.54 = 170.18 cm
- Convert weight: 154 × 0.45359237 = 69.85 kg
- Multiply: 170.18 × 69.85 = 11,887.1
- Divide by 3600 and take the square root: sqrt(11,887.1 ÷ 3600) = sqrt(3.3020) = 1.817
Result: BSA ≈ 1.82 m²
Mosteller BSA for sample height and weight combinations
| Height (cm) | Weight (kg) | BSA (m²) |
|---|---|---|
| 150 | 50 | 1.44 |
| 160 | 60 | 1.63 |
| 170 | 70 | 1.82 |
| 180 | 80 | 2.00 |
| 190 | 85 | 2.12 |
| 200 | 100 | 2.36 |
Common BSA estimation formulas
| Formula | Year | Notes |
|---|---|---|
| Mosteller | 1987 | Simplest, square root based, used by this tool. |
| Du Bois and Du Bois | 1916 | The classic original, still widely cited. |
| Haycock | 1978 | Often preferred for infants and children. |
| Gehan and George | 1970 | Derived from a large measured sample. |
Common mistakes to avoid
- Mixing up the units. The Mosteller formula expects height in centimeters and weight in kilograms. Plugging in inches or pounds without converting gives a wildly wrong answer. Use the imperial toggle so the conversion is handled for you.
- Treating the estimate as an exact measurement. BSA from any formula is a population based estimate, not a direct measurement. Different formulas can differ by a few percent, so do not read more precision into the figure than it carries.
- Using this result for drug dosing. Clinical dosing follows strict protocols about which formula to use, how to round and how to cap the result. Never set or adjust a medication dose from a general calculator. Leave that to a clinician.
- Forgetting children need different handling. Mosteller works for adults and older children, but infants and small children are often estimated with the Haycock formula. The numbers from a generic adult tool may not suit very young patients.
Glossary
- Body surface area (BSA)
- The total area of the outer surface of the body, estimated from height and weight and reported in square meters.
- Mosteller formula
- A 1987 equation that estimates BSA as the square root of height in cm times weight in kg divided by 3600.
- Square meter (m²)
- The unit BSA is reported in. Most adults fall between roughly 1.5 and 2.0 square meters.
- Du Bois formula
- An older, more complex BSA equation from 1916 that the Mosteller formula closely approximates.
Frequently asked questions
What is body surface area?
Body surface area is an estimate of the total external area of the body, expressed in square meters. Because it tracks body size better than weight alone for many physiological processes, it is widely used in medicine, for example to help calculate certain drug doses.
What is the Mosteller formula for BSA?
The Mosteller formula is BSA in square meters equals the square root of height in centimeters multiplied by weight in kilograms, divided by 3600. It is popular because it is easy to compute yet stays close to older, more complex equations.
How do I calculate BSA for 170 cm and 70 kg?
Multiply 170 by 70 to get 11,900, divide by 3600 to get about 3.306, then take the square root, which is about 1.82. So a person who is 170 cm and 70 kg has a body surface area of roughly 1.82 square meters.
What is a normal body surface area?
There is no single normal value, but most adults fall somewhere between about 1.5 and 2.0 square meters. The figure rises with both height and weight, so taller and heavier people naturally have a larger BSA.
Which BSA formula is most accurate?
No formula is exact, since all are statistical estimates. Mosteller and Du Bois are the most commonly used for adults and agree closely. Haycock is often preferred for children. For clinical use the choice is set by local protocol rather than by which is best in general.
Can I use this BSA result for medication doses?
No. This tool is for general understanding only. Drug dosing follows strict clinical rules about the formula, rounding and any dose caps. Always rely on a qualified clinician and the values in your medical records rather than a general calculator.
Sources
- Simplified Calculation of Body-Surface Area (Mosteller, R.D.) , New England Journal of Medicine (1987)
- Body surface area , National Cancer Institute Dictionary of Cancer Terms